Seneca Sawmill Co. announced Friday it has started a $60 million upgrade of its west Eugene lumber mill.

Paving crews were flattening a corner lot of Seneca’s Highway 99 mill site Friday to prepare for construction of two dry kilns, part of what Seneca described as a “major investment” in the company’s future. “This upgrade will allow us to continue improving our sawmill capabilities, and get more lumber out of the tree,” Seneca General Manger Todd Payne said.

Founded by Aaron Jones in 1954, Seneca has grown from a 25-employee outfit producing 18 million board feet of lumber per year to a 450-employee operation with capacity for 650 million board feet today.

By spring, the addition will double the number of dry kilns that Seneca uses to process dimensional lumber — strips of Douglas fir up to 28 feet long, far longer than the 8- to 10-foot lumber fed through its stud mill. Dimensional lumber is ideal for building large commercial and industrial buildings, Payne said, while wood from the stud mill is used mainly for home construction.

The company doesn’t disclose its revenue, and Payne declined to say how many board feet of lumber the mill is producing. But, he said, demand has risen steadily since the depths of the Great Recession. Seneca’s buyers from across the country are increasingly asking for kiln-dried lumber instead of “green” lumber, which contains more moisture and is prone to shrink as it dries naturally. With the upgrades, “we’re investing in our ability to move a greater portion of our product to dry lumber,” Payne said.